MERV, or Minimum Efficiency Reporting Value, is a scale to measure the efficiency of the HVAC unit. Developed in 1987 by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) to check and report the effectiveness of air filters. Their measurement process is more accurate and detailed than other ratings.

The measurement scale provides a numerical value with 1 as the lowest and 20 as the highest efficiency. MERV calculates how effectively an air filter can restrict pollutants, dust, and other minute particles from entering the home.

Clean and pure air is vital for indoor equipment because polluted air can lead to health concerns for you and your family.

If you plan to buy an HVAC product and check filter effectiveness, the MERV method is the best currently. Let’s understand this in detail.

MERV Ratings For Air Filter and Efficiency

MERV ratings for the air filter should be according to the manufacturer's recommendation. You can also ask the technician about a suitable air filter for the home. Only a higher MERV rating does not guarantee a comprehensive comfort level. On the contrary, it can impair performance.

Some high MERV-rated filters come with minor pores that restrict airflow. The product will perform below expectations if the filter is used with an HVAC unit not equipped to manage this resistance. Low efficiency will put more pressure on the machine and affect the indoor atmosphere.

MERV (Minimum Efficiency Reporting Value) is a standard used to rate air filters' effectiveness. The higher the MERV rating, the more effective the air filter is at trapping small particles.

Air filters with a MERV rating of 1 to 4 are considered low efficiency and are typically used in residential and commercial HVAC systems. These filters are effective at trapping larger particles, such as dust and pollen, but are not very effective at trapping smaller particles, such as mold spores and pet dander.

Air filters with a MERV rating of 5 to 8 are considered medium efficiency. These filters effectively trap larger and smaller particles, such as pet dander and some smoke.

Air filters with a MERV rating of 9 to 12 are considered high efficiency. These filters are very effective at trapping smaller particles, such as bacteria and viruses, and larger particles, such as dust and pollen.

Air filters with a MERV rating of 13 to 16 are considered very high efficiency and are typically used in hospitals and other specialized settings. These filters effectively trap microscopic particles such as viruses and tobacco smoke.

It is important to note that while air filters with higher MERV ratings are more effective at trapping small particles, they may also have a higher resistance to airflow. This can put a strain on your HVAC system and may result in increased energy consumption. It is important to select an air filter with an appropriate MERV rating for your specific needs.

MERV and Air Quality

ASHRAE published a research paper that claims the air filter provides several health benefits. There is a direct relation between contaminants and pollutants in the outside air and illnesses indoors. Air filters throw away pollutants and ensure a healthy atmosphere inside.

Key points of the research paper:

The right air filter can be 'modestly effective' for different allergies and symptoms of asthma
The air filter also lowers disease transmission inside the home consistently by restricting pollutants outside
Better particle filtration means lesser exposure to the minute particles below 2.5 µm in diameter
Using the MERV rating chart to understand the filters and their applications.

Contaminant Size Intervals

To get the right HVAC product and suitable MERV-rated air filter, you should know the area you want to use. Refer below to four average contaminant size intervals for MERV rating consideration.

Pollutant Size

Categories Pollutant

0.3-1.0 μm

Smoke, dust, oil smell, bacteria, sneeze droplets

1.0-3.0 μm

Car emissions, bigger dust particles (lead), Legionella

3.0-10.0 μm

Cat/dog dander, Mold spored, mite debris, Hair spray, fabric protector,

10.0+ μm

Pollen, sanding dust, cockroach debris, textile fibers

MERV Ratings and Specific Pollutant Size

We have mentioned the most overall ratings for your reference below.

MERV Ratings

Pollutant Size and Efficiency

MERV 1-4

Less than 20% for 3.0-10 μm particles

MERV 6

49.9% for 3.0-10.0 μm particles

MERV 8

84.9% for 3.0-10.0 μm particles

MERV 10

85% for 3.0-10.0 μm particles, or greater/50% – 64.9% for 1.0-3.0 μm particles

MERV 12

90% for 3.0-10.0 μm particles, or greater/80% – 89.9% for 1.0-3.0 μm particles

MERV 14

90% for 1.0-3.0 μm particles, or greater/75% – 84% for 0.3-1.0 μm particles

MERV 16

75% for 0.3-1.0 μm particles or greater

The MERV scale gives ratings on a scale of 1 to 20. We have mentioned prominent ratings up to 16, where a higher number means more efficient filtering of minute particles. Air filters above 16 ratings are categorized as High-Efficiency Particulate Arresting (HEPA).

MERV Ratings Test Procedure

MERV air filter efficiency rating method is known as ASHRAE Standard 52.2. The procedure tests particle size, and Standard 52.2 facilitates a protocol for testing.

The MERV test starts with a clean filter and contains six cycles. A predetermined quantity of dust particles is released into the airflow during each test cycle.

The test procedure for determining MERV ratings involves drawing air through a sample air filter and measuring the efficiency with which the filter removes particles of a specific size range from the air. The test is conducted using an air filter testing chamber equipped with a fan that draws air through the filter at a specific flow rate.

The test procedure involves introducing a specific concentration of particles into the test chamber and measuring the concentration of particles on the downstream side of the filter. The particle size range and concentration are based on the MERV rating being tested. For example, a filter being tested for a MERV 8 rating would be tested with particles ranging in size from 3 to 10 micrometers and a concentration of approximately 500 particles per cubic foot of air.

The filter's efficiency is calculated by comparing the concentration of particles on the downstream side of the filter to the concentration of particles on the upstream side. The resulting efficiency is reported as a percentage and is used to assign a MERV rating to the filter.

It is important to note that the MERV rating only reflects the filter's efficiency at removing particles within a specific size range. The actual effectiveness of the filter at removing particles of other sizes may be different.

The dust particles are kept in three size groups;

E1: Range 1 to 4 contains particles 0.30 to 1 micron in size
E2: Range 5 to 8 includes particles 1 to 3 microns in size
E3: Range 9 to 12 with particles 3 to 10 microns of size

In each cycle amount of dust particles retained and missed calculated. The procedure is repeated six times. The worst keeper of particles among E1, E2, and E3 during each of the six cycles is considered for the MERV ratings. MERV stands for Minimum Efficiency Rating Value, so the poorest performer is measured for MERV ratings.

Conclusion

We hope our analysis of the MERV ratings chart and procedure will clarify your doubts about checking the air filter's efficiency. Refer to the passage, read the product specifications, follow the manufacturer's guidelines about the required MERV rating for your home, and make the final decision about an HVAC product for the convenience round of the year.

Related Articles You May Like